Chibnall's first short play was produced as part of Contact Theatre's Young Playwright's Festival in 1988, directed by Lawrence Till. While studying at college, he wrote two plays which were performed at the Edinburgh Fringe Festival. In 1998, he became Writer In Residence with GRiP Theatre Company, writing three full length plays, including Best Daze and Gaffer! and several short plays. Chibnall's successor as Writer in Residence was Matthew Broughton.

Chibnall took part in an attachment at the Royal National Theatre Studio in 1999, followed by a year-long attachment to Soho Theatre in 2000, which resulted in his play Kiss Me Like You Mean It, produced at Soho Theatre and directed by Abigail Morris. Its cast included Catherine McCormack, Jason Hughes, Marlene Sidaway and Harry Towb. The play was shortlisted for the Meyer-Whitworth Award, and has subsequently been produced in various venues around the world, including a successful three month run in Paris in 2004.

Gaffer! was revived at Southwark Playhouse in 2004.

Chibnall's first produced script for television was the successful monologue Stormin' Norman, starring James Bolam, made by Carlton Television for ITV.

In 2001 he was approached to develop the format for a drama series which became Born and Bred. A period drama set in the 1950s, the drama was part of a slate of popular drama series overseen by the new Head of Drama Jane Tranter, which also included Spooks and Cutting It. With a cast including James Bolam and Michael French, Born and Bred ran successfully on BBC One for four years from 2002 to 2005, with Chibnall serving as head writer and consultant producer (later executive producer), writing seventeen of its thirty six hourlong episodes.

Chibnall was the only writer other than the show's creators to write for both series of the double International Emmy award-winning BBC One police drama Life on Mars (2006—2007). He was part of the production team who accepted the 2007 BAFTA Audience Award onstage at the London Palladium.

During 2005, Chibnall was in charge of developing a proposed fantasy series involving the mythical magician Merlin for BBC One's early Saturday evening family drama slot. However, despite several scripts being written, BBC Head of Drama Jane Tranter eventually decided not to green-light the project, although it later emerged, without Chibnall’s involvement, as Merlin (2008—present).

In 2005, Chibnall was appointed head writer and co-producer of science-fiction drama Torchwood. The series, a spin-off from the long-running Doctor Who, premiered on BBC Three in October 2006 to a then record-breaking audience for a digital channel in the UK. The programme went on to win "Best New Drama" at the 2007 TV Quick Awards and "Best Drama Series" at the BAFTA Cymru 2007 awards. The series has also been nominated for both Hugo and Saturn awards. "Torchwood" (2006) - Awards In the USA, the programme has been broadcast on BBC America and HDNet, to critical acclaim. Search Results from Metacritic.com Chibnall wrote eight episodes during the first two series, including both series finales, and the premiere episode of series two. He worked closely with Russell T Davies across all aspects of the show's production.

While working on Torchwood, Chibnall also penned the 2007 episode "42" for the third series of "Doctor Who". The series won the Writers Guild of Great Britain award for Best Series that year.

Chibnall is a long-time fan of Doctor Who, and appeared on the BBC discussion programme Open Air in 1986 as a representative of the Doctor Who Appreciation Society, criticising the quality of the series at the time.

In 2007, Dick Wolf and Kudos Film and Television selected Chibnall to become the show runner on ITV1’s UK, a police procedural/legal drama based on the original US series. Chibnall was the lead writer and executive producer, writing six of the first thirteen episodes based on scripts from the US series. Chibnall was responsible for the overall creative direction of the UK show, including story selection, casting and post-production, working closely alongside other executive producers Jane Featherstone, Andrew Woodhead and Dick Wolf. The series premiered its first seven episodes in February 2008 to strong ratings and critical response. A further six episodes were transmitted, beginning in January 2009. ITV has commissioned a second run of thirteen episodes. Having set up the series, Chibnall made the decision to leave the programme after one series, to focus on other writing projects.

Chibnall is also currently showrunning Camelot, an adult retelling of the Arthurian legend for the Starz network. It is expected to air early next year and is being filmed in Ardmore Studios near Dublin.